Windows, such as those used in commercial and residential buildings, have long been a source of energy loss and are therefore associated with significantly increased energy costs. Despite efforts in the last three decades to reduce energy costs associated with windows, an estimated 2.7 quadrillion BTU's of energy utilized to heat and cool buildings in the United States in 2006 (out of estimated total of 10 quadrillion BTU's expended) were attributable to windows, an amount roughly equivalent to the nation's entire Strategic Petroleum Reserve. Energy inefficiencies associated with windows include heat loss through the window in cold weather, heat gain through the window in hot weather, or both.
Many technologies that reduce energy losses from windows have developed in the past few years. For example, today's windows can employ multiple glazing, high-tech materials like aerogel between the glazing, and low-emissivity (low-E) coatings to minimize heat loss. There are also coatings that are much more reflective of infrared light than visible light. However, even windows which employ all these advances have significant energy losses. This is because they are designed for single climate use and cannot adapt to changing weather conditions.
Accordingly, there remains a need for variable light attenuating devices, such as windows, that can reduce or minimize the amount of energy loss associated with conventional windows by employing technologies that can use solar energy to minimize or eliminate external power consumption. Such technologies can add energy efficiencies by modulating the amount of sunlight transmission to account for heat gain differences between summer and winter seasons.